In recent years, in-home networks are being realized in which domestic digital devices are connected to a network, and digital contents (referred to as “content” hereinafter) of various kinds are shared between the devices with the use of such networks.
Meanwhile, such contents as newly distributed movies and pay-per-view television programs need to be protected under copyright laws. One major means as to realize copyright protection of such contents is encryption of contents prior to transmission over the network. This technology is standardized in the DTCP-IP (Digital Transmission Content Protection over Internet Protocol) protocol.
The DTCP-IP protocol provides an authentication key exchange function compliant with AKE (Authentication and Key Exchange) and a key revocation function. Provided with such functions, DTCP guarantees safe reception of contents on authorized digital devices, while preventing fraudulent use of contents by unauthorized devices.
In addition to the above, the DTCP protocol establishes a higher extent of copyright protection by defining a technology in which transmission/reception of contents by unauthorized devices is further restrained through providing a list of unauthorized devices (specified as CRL [Certificate Revocation List] by the DTCP protocol) to each individual authorized digital device.
The unauthorized device list is distributed to each digital device by the DTLA (Digital Transmission Licensing Administrator). The unauthorized device list is subject to be updated every time a device deemed to be incompliant to the DTCP protocol is newly found and thus, a newly manufactured digital device may have a more recently updated version of the unauthorized device list compared with the unauthorized device lists held by devices manufactured earlier.
With the unauthorized device list having such characteristics, DTCP-compliant digital devices mutually exchange information on the unauthorized device lists they hold when performing transmission/reception of contents. When a list held by a local device is determined, according to the information exchanged above, to be older than a list held by a target device, the local device receives the newer list from the target device and updates the list to the newer list.
In relation to the present invention, Patent Literature 1 discloses, as a technology of exchanging the unauthorized device list, a technology of updating the unauthorized device list held by devices in a topology to the newest version on a constant basis by utilizing topology connection information.